Many people with chronic pain swear by acupuncture, but skeptics of the ancient needle-based treatment have long claimed that it's little more than an elaborate placebo.

A new study published this week in the Archives of Internal Medicine appears to at least somewhat vindicate the acupuncture believers.

After re-analyzing data from 29 high-quality clinical trials dating back to the 1990s, researchers have concluded that the pain relief derived from acupuncture is partly real, in that it can't be ascribed entirely to the placebo effect.

The trials, which included roughly 18,000 people with chronic pain stemming from arthritis, headaches, or back and neck problems, all compared genuine acupuncture with one of two alternatives: treatment as usual, or "sham" acupuncture -- a counterfeit (i.e. placebo) version of the treatment in which needles are inserted unsystematically.

Pain relief of 50% or more on a 100-point scale -- pain that drops from a 60 to a 30, say -- is a commonly used standard of effectiveness in pain research. By this measure, the study found, the effectiveness rates for real acupunture, sham acupuncture, and treatment as usual are 50%, 43%, and 30%, respectively.

Acupuncture, which originated in China, involves placing needles in specific locations or "meridians" of the body in order to treat various ailments, especially pain. Acupuncture practitioners claim the technique relieves pain by modifying energy flow through the body.

The energy-flow theory has met with a great deal of skepticism in the United States and other Western nations, and researchers have failed to identify other, biological underpinnings for the treatment.

Dozens of clinical trials have sought to prove that acupuncture is more than a placebo by comparing the real thing with sham treatments, which in addition to misplaced needles can include electrical or laser stimulation designed to mimic pinpricks.

The new study bolsters the evidence for acupuncture but doesn't quite put to rest the idea that patients are largely responding to the placebo effect, says Dr. Andrew L. Avins, an epidemiologist at the University of California, San Francisco and a research scientist at Kaiser Permanente, a large nonprofit health plan based in Oakland, California.

Although genuine acupuncture clearly benefited the study participants, Avins says, the fact that the effectiveness rate was much higher than treatment as usual but only slightly higher than the sham treatment suggests that most of the benefit associated with acupuncture is indeed attributable to the placebo effect.

What's more, he adds, the modest difference between genuine and sham acupuncture may not be meaningful for the average real-world patient.

"Acupuncture does appear to have some very small benefit above and beyond placebo acupuncture or sham acupuncture," says Avins, who wrote an editorial accompanying the study. "But the effects really are pretty small, and the majority of the effect is a placebo effect."

Acupuncture skeptics will likely seize on this point, Avins says, but the study findings don't mean that acupuncture doesn't work, or that doctors shouldn't refer pain patients for the treatment.

Acupuncture, he suggests, should perhaps be viewed as a way of providing modest pain relief while also harnessing the placebo effect.

"In the past, people have viewed placebos as negative things, (but) they could have some real benefits for patients," Avins says. "I would be hard-pressed to tell a patient who says they're benefiting from something that's 'just a placebo' to stop using it."